The invention relates to a differential hydraulic machine, particularly a differential hydraulic motor, of the kind comprising:
an envelope;
a differential piston capable of sliding in a reciprocating movement in the envelope, the piston having two parts of different diameters capable of moving in two corresponding chambers of the envelope;
hydraulic switching means for supplying and evacuating the respective chambers, these switching means being driven by the piston and able to adopt two stable positions relative to the piston;
control means for an abrupt change in the position of the switching means relative to the piston, comprising elastic means capable of storing energy;
and triggering means capable, at the end of the stroke of the piston, of releasing the energy stored by the elastic means and of causing the abrupt change in position of the switching means, these triggering means comprising thrusting means which, at the end of the piston stroke, come to bear against stops which are fixed relative to the envelope.
A differential hydraulic motor of this type is known, for example, from EP-B-0255791 or from U.S. Pat. No. 5,505,224, and can be used as a device for injecting an additive into a main fluid. The elastic means consist of springs, the size of which is small by comparison with the components that make up the mechanism as a whole. These springs act transversely to the direction of travel of the piston and require transmission means of the connecting rod type, mounted so that they can rotate about axes of rotation which are generally orthogonal, or at least secant, to the lines of action of the forces developed by the springs.
FR-A-2619165 discloses a hydraulic motor which, according to the alternative form in FIG. 2, comprises elastic means exerting force along the geometric axis of movement of the piston. The spring is arranged around a rod inside a frame equipped, on its longitudinal sides, with sets of teeth collaborating with pinions controlling an eccentric and a connecting rod system. Arranging the spring along the axis of the piston allows simplification as regards the transmission of the forces exerted by this piston, but the spring remains small in size and the entire system is relatively complicated.
There is also disclosed, in DE-A-19728179, a hydraulic motor comprising a reciprocating differential piston which reverses automatically, particularly for a volumetric metering device. According to that document, the motor does not have controlled locking means, which means there is no sequential switching to guarantee repeatability and reliability. Locking is essentially hydraulic and switching is caused only by equilibria of pressure generated by direct action on sealing elements. The springs provided in that motor do not directly bring about the switching.
EP-A-0161614 discloses a differential hydraulic motor in which the triggering means comprise connecting rods subjected to the action of transversely arranged elastic means. The change in position of the valves and the reversal of the movement occur with impact of a spindle against some other component. These impacts are a source of noise and are detrimental to motor life.
U.S. Pat. No. 5,513,963 discloses a differential hydraulic motor in which the locking system is passive, that is to say not controlled. Switching is brought about only by direct action of the springs on the sealing elements which end up balancing the holding forces that result from the locking and from the hydraulic effects. Such a design does not make it possible to store up more energy than the energy capable of breaking the equilibrium.
The object of the invention is, above all, to provide a hydraulic machine, particularly a differential hydraulic motor, which is of simple construction while at the same time having elastic means exerting force along the geometric axis of movement of the piston and which makes it possible to reduce the friction caused by the spring load and the guiding surfaces. The invention also aims to extend the life of the devices by reducing component wear. The efficiency and speed of operation of the machine are also to be improved. The design of the machine has to allow sequential switching, which guarantees repeatability and reliability, and to allow more energy to be stored than is capable of breaking equilibrium, so as to have a high operating margin.
According to the invention, a reciprocating differential hydraulic machine, particularly a differential hydraulic motor, of the kind defined previously, comprises elastic means exerting force along the geometric axis of movement of the piston, and is characterized in that:
the switching means are carried by a lantern ring with a side wall coaxial with the piston, driven by this piston but capable of adopting two different stable positions relative to the piston,
and the elastic means are arranged on the outside of the lantern ring and are guided internally by the side wall of this lantern ring.
Advantageously, the elastic means comprise a spring coaxial with the lantern ring and surrounding it. In particular, the spring is a helical compression spring.
This spring may thus have a large diameter and a large wire cross section, making it possible to obtain good operational flexibility. The large cross section of the wire of the spring gives it good resistance to corrosive wear.
As a preference, the lantern ring is guided in its lower part by a cylindrical region of the differential piston.
At least one push-rod is provided at each axial end of the lantern ring, the push-rod or push-rods of one end being independent of the push-rod or push-rods of the other end of the lantern ring, these push-rods bearing against the elastic means and being retained axially by stops provided on the lantern ring, which guides the push-rods in a translational movement.
The lower push-rod may have a diametral crossmember equipped with a rod coaxial with the piston, projecting on the opposite side to the elastic means. The rod passes in sealed fashion through a transverse wall of the piston and comes into abutment, at the bottom end of travel, against a transverse bar which bears against a part of the envelope. The bar may be mounted so that it can slide in a support connected to the piston.
The diametral crossmember may be secured to a ring bearing against the lower rim of the lantern ring, this ring surrounding the side wall of the lantern ring which has two longitudinal guide openings through which the crossmember passes.
Two diametrically opposed upper push-rods are provided and are guided by the lantern ring, particularly by longitudinal openings.
The lantern ring may comprise an upper plate equipped, on the inside, with two diametrically opposed cutouts in which the upper push-rods are engaged and slide. The upper plate may be assembled by clip-fastening.
The switching means advantageously comprise valves.
The assembly consisting of the lantern ring, of the elastic means and of the push-rods exhibits axial symmetry of construction guaranteeing that the various forces involved are in equilibrium, and making it possible to reduce risks of jamming.
The lantern ring is advantageously held stable in one of its two positions relative to the piston by a device of the toggle-joint type, with three axes, comprising a connecting rod and a trigger.
The connecting rod is articulated at one end to the upper plate of the lantern ring and at its other end to the trigger; the trigger is itself articulated to a component connected to the piston.
The trigger comprises two diametrically opposed extensions capable of coming into abutment against a stop connected to the piston, respectively above and below this stop following rotation through about 180xc2x0, each extension of the trigger being capable of collaborating with a projection provided respectively on an upper push-rod and on a lower push-rod so as to trip the trigger when the elastic means are under sufficient load.